Organic Light Emitting Display (OLED) has the advantages of self-luminous, low driving voltage, high luminous efficiency, short response time, sharpness and contrast, nearly 180° viewing angle, wide temperature range, flexible display and large-area full-color display. It is recognized as the most promising display device in the industry. According to the driving mode, the OLEDs can be divided into two types: a passive matrix OLED (PMOLED) and an active matrix OLED (AMOLED), namely direct addressing and thin film transistor (TFT) matrix addressing two categories. Wherein, AMOLED has a matrix arrangement of pixels, belonging to the active display type, high luminous efficiency, usually used for high-definition large-size display device.
The pixel driving circuit of the existing OLED panel generally includes a switch TFT, a driver TFT and a storage capacitor (Cst). The switch TFT is controlled by a scanning signal for controlling the data signal. The driver TFT is used for controlling the current passing through the OLED. The storage capacitor is generally used for storing the grayscale voltage to determine the driving current of the driver TFT.
As shown in FIG. 1, FIG. 1 is a structure diagram of the existing OLED panel. It can be divided by the function area into a switch TFT area, a driver TFT area and a storage capacitor area. The existing OLED panel mainly includes: a glass substrate 10; a light shielding layer (LS) 11 deposited on the glass substrate 10; a buffer layer 12 depositing on the light shielding layer 11; a semiconductor layer 13 deposited on the buffer layer 12, wherein the semiconductor layer 13 may be amorphous oxide semiconductor (AOS), and the area of the semiconductor layer 13 contacted with the TFT electrode can increase the doping concentration, for example, can form a N+ conductor layer; a gate insulating layer (GI) 14 deposited on the semiconductor layer 13; a first metal layer 15 (i.e. gate metal layer) deposited on the gate insulating layer 14 for forming a gate (G) of the TFT; an interlayer insulating layer (ILD) 16 deposited on the first metal layer 15; a second metal layer 17 (i.e. source-drain metal layer) deposited on the interlayer insulating layer 16, wherein the second metal layer 17 is pattered to partially form a source (S) and a drain (D) of the TFT and partially form a storage capacitor (corresponding to the storage capacitor area); a passivation layer (PV) 18 deposited on the second metal layer 17, wherein the passivation layer 18 in the prior art is generally made of SiOx; a color filter (CF-RGB) 19 formed on the passivation layer 18; a planarization layer (PLN) 40 formed on the color filter; an anode 41 deposited on the planarization layer 40, wherein the anode 41 may be a transparent oxide such as indium tin oxide (ITO); a pixel defining layer (PDL) 42 formed on the anode 41 for determining the light emitting area of the OLED device; a light emitting layer 43 formed on the anode 41 by vapor deposition or ink jet printing (IJP); and a cathode 44 formed on the light emitting layer 43. Others such as package structure will not be repeated here.
In the current top gate oxide TFT design, the storage capacitor is made of a structure of Indium Tin Oxide (ITO)-Metal 2-Amorphous Oxide Semiconductor (AOS). However, due to the interlayer between the Metal2 and the ITO is the passivation layer (PV) and the planarization layer (PLN) (shown in FIG. 1), the thickness of the two layers are larger. The storage capacitance is small when the area is the same. In order to achieve the need to increase the storage capacitance can only increase the area of the storage capacitor, it will seriously affect the aperture ratio.